| Abstrakt: |
Located on the outskirts of the Sydney metropolitan area, Berowra Creek is an estuarine tributary of the Hawkesbury River with high environmental and recreational values. Ongoing water quality issues in the estuary, including algal blooms, have been recorded over the past decades. Sydney Water upgraded two treatment plants in the catchment to the tertiary level, which incorporated additional nutrient removal and disinfection processes. In 2015, the Galston and Glenorie Priority Sewerage Program expanded the sewer network in the catchment to centralise wastewater treatment. These works have significantly reduced the nutrient load entering the waterway environment. Nevertheless, algal blooms still occur within the system, remaining a concern for the community and relevant stakeholders. This investigation aimed to assess key factors contributing to the water quality issues affecting the health of the aquatic system. It is part of the ongoing development of the Water Quality Response Models of the Hawkesbury Nepean River system, which are considered a key strategic capital asset for Sydney Water. A 3D TUFLOW FV model, together with its Sediment Transport and Water Quality Modules, was used to simulate hydrodynamic conditions and biogeochemical processes, enabling the evaluation of relevant environmental processes and impacts. The model captures nutrient inflows from wastewater treatment plants, septic systems, catchment runoff and tidal flushing. The modelling reveals that, while tidal flow provides significant flushing in the estuary, the presence of deep holes in the channel bed near Calabash Bay substantially slows water movement and increases residence time. This process creates favourable conditions for the accumulation of nutrient-rich sediment, promoting the algal growth. Estuarine stratification further increases residence time and can create stable conditions for the growth of phytoplankton. These findings highlight the challenges posed by the unique bathymetric and hydrodynamic conditions and provide insights for future environmental and water resources management in Berowra Creek Estuary. The calibrated and validated water quality response model serves as a tool for impact assessment and enables planning and catchment management scenario analysis. [ABSTRACT FROM AUTHOR] |
